This project involves genetic analyses of simian virus 40 and adenovirus type 5. In the simian virus 40 system, deletion and mutations are being introduced at putative control regions on the viral chromosome (the origin of DNA replication and near the 5'-termini of mRNAs) and the physiological effects of these mutants are being studied. In the adenovirus type 5 system, deletion mutations have been introduced within the portion of the viral chromosome required for transformation. Again, the physiological effects of these mutations are under study.